Automatic number identification (ANI) systems have been used in telephone switching equipment for many years to properly and automatically bill long distance toll charges to the appropriate calling parties. Automatic recording and processing of the directory number of the calling subscriber was developed by the Bell System. This allowed centralized automatic message accounting for long distance calls. The identity of the calling line is determined by ANI circuits installed in a central office equipment, along with automatic message accounting equipment.
Central office ANI equipment is an integral part of the central office equipment and uses identifier circuits to trace the connection from the calling party to the called party using an identification tone applied to the connection and tracing the tone. When the tone is traced to the called subscriber's line, an out-pulser is invoked to transmit using multi-frequency (MF) tones the called subscriber's number to the calling subscriber's central office equipment. When all of the digits have been transmitted, the telephone line is cut through for talking and the centralized automatic message accounting system reports the called party's number in the central office of the calling party for later billing. Thus, the local central office of the calling subscriber records both the telephone number of the called party and the telephone number of the calling party. However, the central office of the called party or the called party himself/herself is unaware of the directory number of the calling party.
A reverse automatic number identification system has been developed for local use between local central offices for the 911 emergency system. The automatic number identification equipment in the local central offices are utilized to locate the telephone directory number of the calling party and transmit it using multi-frequency tones to the 911 operator, where it is displayed on a CRT screen or printer.
The present invention is designed to provide reverse automatic identification of the calling subscriber's telephone number to the called party by means of reverse ANI equipment installed in central offices and installed in customer premises which does not interfere with the normal operations of the central office ANI equipment. This "add-on" equipment operates either locally or over long distances to provide the area code, telephone number and type of calling subscriber (e.g., business, residential, pay phone, etc.) to the called party. Reverse automatic number identification equipment for use by subscribers is unknown in the prior art.